Thin-section photomicrograph (plane-polarized light) of a near-back-reef
grainstone in the
Tansill Formation. The predominant grains again are Mizzia green algae but
in this example,
the primary porosity was partially filled with an early diagenetic cement
produced in the vadose
zone  note slight corrosion of tops of grains and pendants or microstalactites
of calcite cement
below the grains. Subaerial exposure may have occurred on small islands during
sedimentation
or in association with a major (early Ochoan) hiatus that follows Tansill
deposition. Sample
from Walnut Canyon (New Mexico Highway 7), less than 1 km west of the canyon
mouth,
Carlsbad Caverns National Park, Eddy Co., NM. Long axis of photo = 6 mm.